Many of the genes expressed in brain are also expressed in other tissues. However, in addition to the shared transcripts, and equal number of both nonadenylated and adenylated polysomal RNAs are uniquely transcribed in adult brain. The significance of the nonadenylated polysomal RNA transcripts is unclear. They may be a new class of brain messenger RNAs potentially regulated in a unique fashion, a class of RNAs of unknown function, or merely a trivial end product of RNA metabolism in brain. To differentiate between these possibilities, we shall identify and characterize clones from recombinant DNA libraries that contain sequences representative of this class. The function of the adenylated polysomal RNA class is clear; it is composed of translationally active messenger RNAs. Little is known about the transcriptional patterns of members of this class that may distinguish one brain region or even one neuronal cell type from another. We shall determine the extent to which different polyadenylated messenger RNA are cell type-specific in a well characterized brain region, the rat cerebellum. We shall also identify and characterize messenger RNAs present only in developing cerebellum. Sequences belonging to both these classes will be identified in recombinant DNA libraries. The distribution of the transcripts in developing and adult cerebellum will be contrasted with that for the mRNA encoding glutamic acid decarboxylase, the rate limiting enzyme for the synthesis of a neurotransmitter. Once transcripts that are either uniquely nonadenylated, cell type-specific, or developmentally regulated have been characterized, we shall identify the genomic sequences regulating their expression. The first step will be to sequence the messenger RNAs. The corresponding genomic clones will be identified and partially sequenced. Putative control sequences will be fused to a reporter gene, and the constructs tested for correct expression in transgenic mice. Completion of these specific aims will provide a baseline of information necessary for determining the mechanisms by which gene expression is regulated in the brain.